214 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1954 



both in Europe and in America, the large radial air-cooled engine, 

 pioneered in America by Charles L. Lawrance. During development 

 in the use of the water-cooled upright engine, like the Liberty, it 

 became increasingly apparent that whereas the Wrights had good 

 reason for the upright engine in order to have their chain-drive mount 

 on the wing, the later water-cooled tractor types of aircraft should 

 have started out right then and there as inverted engines with the 

 crankshaft high, in order to give maximum propeller clearance for 

 minimum body height. 



The problem of radiator cooling was not solved until the advent 

 of the air-cooled engine. The disadvantage of the liquid-cooled engine 

 was especially evident in war planes ; one bullet hitting the radiator 

 could wreck the whole mechanism, whereas several cylinders of an air- 

 cooled engine could be damaged without causing the engine to stop at 

 once. Through the years radiators assumed all manner of shapes, 

 sizes, and configurations; they were placed in front of the engine, 

 behind the engine, above the engine, slung underneath, formed into 

 wing surface contours, and so on. The Wrights started out with a 

 simple vertical combination of standpipes that had a large cooling 

 area for the water volume and — a very important item — a large gravity 

 head over the water pump. The weight of the water-cooling system 

 was mitigated somewhat in later years by the use of chemicals for 

 cooling, but the extra plumbing and the extra drag always remained. 

 There were many sighs of relief when air-cooled engines came into 

 use, and an even greater sense of relief now that we have entered into 

 the jet era, with a simple, easy-to-install power plant. 



MATERIALS AND CONSTRUCTION 



The materials used in construction of aircraft have, of course, varied 

 considerably through the years. At first silver spruce was used by 

 the Wrights and others in wing spars, struts, ribs, etc. ; ash was used 

 for the skids as it was a much harder wood. But the generally unsatis- 

 factory nature of wood — the difficulty of getting pieces of the same 

 weight and even of the same strength that could be relied on, and 

 weather changes — all affecting the strength or alignment of the struc- 

 ture, were headaches that quite naturally led, both in Europe and in 

 this country, to the consideration of metal construction. At first this 

 was thought to be too heavy, but it was not long before it was discov- 

 ered that very thin high-alloy steel tubings gave a weight ratio to their 

 strength that was satisfactory. At first the joints were made with 

 fittings, and later were brazed and soldered ; then the Fokker type of 

 welded-tube construction came into wide usage, particularly in the 

 framework of fuselage and tail surfaces. Wing surfaces were covered 

 with oiled silk or rubberized fabric, but both of these materials were 



